1. Field of the Invention
The present invention relates to the improvement of HSG (Hemispherical silicon grain), and more specifically relates to preventing the cluster defect of HSG by heat treatment.
2. Description of the Prior Art
HSG is broadly applied in contemporary semiconductor fabrication. The most famous application of HSG is forming HSGs on surface of bottom electrode of capacitor to efficiently increase total surface area of electrode of capacitor.
In addition, in most of applications of HSG, when HSGs (Hemispherical Silicon Grains) are formed on a wafer, then wafer with HSGs are directly cleaned before any following fabrication such as deposition of dielectric layer. For example, when HSGs are used to increase surface area of electrode of capacitor, HSGs are pre-cleaned before formation of dielectric layer. Herein, cleaning process is used to wipe out any impurity on the wafer and is more especially to wipe out any impurity on HSGs. No matter how, an obvious defect is found that during cleaning process a plurality of clusters appear on surface of HSGs. In other words, parts of HSGs are covered by these clusters and then yield of following fabrication is decreased by these clusters. No matter how, mechanism of formation of clusters still is an unsolved question, and a main component of these clusters is silicon.
FIG. 1A to FIG. 1C are some qualitative illustrations show how formation of HSG and clusters defect are formed by conventional fabrication.
First as FIG. 1A shows, dielectric layer 12 is formed on substrate 10 and is patterned to form a plurality of gaps inside dielectric layer 12. Therefore, conductive layer is formed on dielectric layer 12 and completely fills all of gaps. Then, conductive layer is patterned to form a plurality of conductive structures 14, where each conductive structure 14 completely fills one gap. In addition, possible material of conductive structures 14 comprises polysilicon, silicon and so on. No matter how, in order to form HSG on conductive structures 14 in following process, it is better to be formed conductive structures 14 by polysilicon.
As FIG. 1B shows, HSGs 16 are formed on conductive structures 14 and main function of HSGs 16 is increasing total surface area of conductive structures 14.
Therefore, HSGs 16 and dielectric layer 12 are directly cleaned just when HSGs 16 are formed, clusters 18 are obviously formed on HSGs 16, as FIG. 1C shows. Where material of clusters 18 comprises Si. In addition, cleaning solution of said cleaning process comprises HF and nitric acid.
The disadvantage of clusters 18 can be explained by an example, as FIG. 1D shows. When oxide layer 19 is formed on dielectric layer 12 and totally covers conductive structures 14 and HSGs 16, it is obvious that the interactive area between HSGs16 and oxide layer 19 is decreased by cluster 18, and then interaction between HSGs16 and oxide layer 19 is degraded by the cluster defect
According to previous discussion, it is obvious that cluster defect is a serious disadvantage in application of HSG and then it is desired to develop a method to overcome the cluster defect.